Should I break it off, or keep being friends?

I have the same exact friend. I honestly know how you feel. We have so much fun together, but when we argue, she is so stubborn that i can't stand her. Mabye you should talk to her about it and tell her about how you dint like her attitude sometimes. If she really is your best friend, and she wants to stay that way, she'll probably want to make some effort to try to repair the relationship.